This application claims the benefit under 35 U.S.C. xc2xa7 119 of Japanese Patent Application Nos. 11-343700 and 2000-350738, the abstract of disclosure of which is incorporated herein by reference.
The present invention relates to an expansion shaft. More particularly, the invention is directed to an improved structure of the expansion shaft for preventing vibrations resulting from play in fit portions of a pair of shaft sections.
The expansion shaft is used as, for example, a steering shaft of an automobile.
The expansion shaft is also used as an intermediate shaft interconnecting the automotive steering shaft and a steering mechanism such as a rack and pinion type mechanism. In this case, the extending function is used for adjustment of the intermediate shaft length for accommodating a relative displacement between a steering gear and a steering column while a vehicle is driven, or used for adjustment of the length of the intermediate shaft at the time of being assembled.
A spline or serration is generally employed as a structure for establishing fitting engagement between the pair of shaft sections of the expansion shaft.
For instance, the two shaft sections may be integrally rotatably joined together by inserting an end of a second shaft section into a fit hole formed at an end of a first shaft section. The fit hole includes a female serration (also called an internal serration) while the end of the second shaft section includes a male serration (also called an external serration).
In this case, the second shaft section cannot be inserted into the fit hole if there is no clearance between the male serration and the female serration. Unfortunately, the clearance has the adverse effect of permitting the shaft sections to be radially or circumferentially displaced relative to each other, thus causing rattle which is annoying to a driver.
For this reason, the second shaft section is configured such that a part of the male serration is cut away to produce a cutaway portion or to define a D-shape in section. With a flat plate spring of a bent form placed on the cutaway portion, the second shaft section is fitted in the fit hole of the first shaft section thereby preventing the occurrence of rattle.
However, the configuration suffers a poor assemblability because of a fear that the plate spring on the cutaway portion of the second shaft section may move out of place when the second shaft section is inserted in the fit hole of the first shaft section. In some cases, the second shaft section may be assembled with the plate spring displaced out of place. This leads to the variations of an anti-rattle effect.
As an approach to overcome this problem, an anti-rattle member as shown in FIG. 8 has heretofor been proposed (Unexamined Japanese Utility Model No.7(1995)-40360). The anti-rattle member is arranged such that one shaft section 51 is formed with a thick shaft portion 52 at an end thereof, which is formed with a male serration 53, while a female serration 54 for fittingly receiving the male serration 53 is formed at an inner circumferential surface of a fit hole 56 of the other shaft section 55. The male serration 53 includes a first portion 53a and a second portion 53b which are axially separated from each other. A thin shaft portion 57 is defined between the first and second portions 53a, 53b and is adapted to be brought into fitting engagement with an anti-rattle member 58.
Referring to FIGS. 8 and 9A-9B, the anti-rattle member 58 includes two legs 59 substantially of an annular shape (C-shape) having a smaller inside diameter than an outside diameter of the thin shaft portion, and a body 60 interconnecting these legs 59 at their mid portions.
When the one shaft section 51 is inserted in the fit hole 56 of the other shaft section 55, the anti-rattle member 58 is stably retained on the one shaft section 51 by way of the legs 59 resiliently clamping the thin shaft portion 57. This eliminates a fear of disengagement of the anti-rattle member 58 during assembly.
The body 60 is of a bent shape raised at its intermediate portion. The body is designed to prevent the occurrence of rattle by way of its top portion resiliently pressing against the female serration 54.
However, the thin shaft portion 57 is increased in the axial length because of the anti-rattle member 58 having the pair of legs 59, 59 axially spaced from each other by a distance D. As a result, the male serration 53 is increased in the overall axial length. Hence, a fit length between the pair of shaft sections 51, 55 is increased so that the overall weight and costs of the expansion shaft increase.
In view of the foregoing, it is an object of the invention to provide an expansion shaft capable of achieving the reduction of size and weight.
In accordance with a preferred aspect of the invention for achieving the above object, an expansion shaft comprises a first and a second shaft section aligned on the same axis, the expansion shaft further comprising a fit hole formed at the first shaft section for receiving the second shaft section; a thin shaft portion defined on the second shaft section; a pair of thick shaft portions formed on the second shaft section as axially sandwiching the thin shaft portion therebetween; a groove and a ridge respectively formed in an inner circumferential surface of the fit hole and on the thick shaft portions for coming into fitting engagement thereby integrally rotatably interconnecting the first and second shaft sections as allowing the shaft sections to axially move relative to each other; and a resilient member interposed between the inner circumferential surface of the fit hole of the first shaft section and an opposite outer peripheral surface of the second shaft section for preventing the shaft sections from radially moving relative to each other. The resilient member includes a single C-shaped snap ring resiliently clamping the thin shaft portion, and an arm extended from the snap ring in at least one axial direction of the second shaft section and serving to press against the inner circumferential surface of the fit hole of the first shaft section.
According to the embodiment, the single C-shaped snap ring is used for retaining the resilient member on the thin shaft portion of the second shaft section so that the thin shaft portion can be reduced in the axial length. This contributes to the reduction of the fit length between the first and second shaft sections, thus enabling the realization of a compact, lightweight expansion shaft. In addition, the arm resiliently presses against the inner circumferential surface of the fit hole of the first shaft section thereby positively preventing the vibrations due to a loose fit between the first and second shaft sections as well as the occurrence of noise associated with the vibrations.